RESEARCH Rapid river incision across an inactive fault—Implications for patterns of erosion and deformation in the central Colorado Plateau Joel Pederson1, Neil Burnside2,*, Zoe Shipton2,†, and Tammy Rittenour1 1DEPARTMENT OF GEOLOGY, UTAH STATE UNIVERSITY, LOGAN, UTAH 84322, USA 2DEPARTMENT OF GEOGRAPHICAL AND EARTH SCIENCE, UNIVERSITY OF GLASGOW, SCOTLAND G12 8QQ, UK ABSTRACT The Colorado Plateau presents a contrast between deep and seemingly recent erosion and apparently only mild late Cenozoic tectonic activ- ity. Researchers have recently proposed multiple sources of epeirogenic uplift and intriguing patterns of differential incision, yet little or no quantitative constraints exist in the heart of the plateau to test these ideas. Here, we use both optically stimulated luminescence (OSL) and uranium-series dating to delimit the record of fl uvial strath terraces at Crystal Geyser in southeastern Utah, where the Little Grand Wash fault crosses the Green River in the broad Mancos Shale badlands of the central plateau. Results indicate there has been no deformation of terraces or surface rupture of the fault in the past 100 k.y. The Green River, on the other hand, has incised at a relatively rapid pace of 45 cm/k.y. (450 m/m.y.) over that same time, following a regional pattern of focused incision in the “bull’s-eye” of the central plateau. The Little Grand Wash fault may have initiated during Early Tertiary Laramide tectonism, but it contrasts with related structures of the ancestral Paradox Basin that are presently active due to salt dissolution and focused differential erosion. We also hypothesize there may be a Pliocene component of fault slip in the region linked to broad-wavelength erosional unloading, domal rebound, and extension. An apparent rapid decrease in incision rates just upstream through Desolation Canyon suggests the Green River here may have recently experienced an upstream-migrating wave of incision. LITHOSPHERE; v. 5; no. 5; p. 513–520; GSA Data Repository Item 2013319 | Published online 3 September 2013 doi: 10.1130/L282.1 INTRODUCTION Several sources of middle-late Cenozoic regional ancestral Paradox Basin. In the cases of the Gra- uplift have been recently proposed for the Colo- bens district of Canyonlands National Park in The Colorado Plateau of the western United rado Plateau. These include buoyancy modifi ca- southeastern Utah and the Onion Creek diapir States is famous for the spectacular erosional tions of the mantle lithosphere linked to an ances- to the north, it has been established that defor- exhumation of a stratigraphic record that has try involving the Farallon slab (e.g., Humphreys mation is ongoing today (e.g., Colman, 1983; been subject to only mild tectonic deformation et al., 2003; Roy et al., 2009), regionalized Huntoon, 1988; Furuya et al., 2007). It also has over Phanerozoic time. Overall erosion of the dynamic support from convecting asthenosphere been widely speculated that localized dip-slip region is linked to a pulse of late Cenozoic inci- and potential mantle drips (Moucha et al., 2009; faulting and E-W–oriented graben formation sion driven by the integration and base-level drop van Wijk et al., 2010; Levander et al., 2011), and continued into the Quaternary or is still active in of the Colorado River off the southwestern mar- isostatic rebound due to unloading by erosion the central plateau (Colman and Hawkins, 1985; gin of the plateau to the Gulf of California (Luc- and extension (Pederson et al., 2002; Roy et al., Doelling et al., 1988; Shipton et al., 2004). The chitta, 1972; Pederson et al., 2002). That plateau 2009; Karlstrom et al., 2012). Indeed, the fl ex- Little Grand Wash and Salt Wash (aka Ten- margin in the western Grand Canyon area is the ural feedback between late Cenozoic exhumation Mile) Graben faults crossing the Green River focus of scientifi c controversy because of its and rock uplift is focused upon the central pla- are examples that have been a focus of recent complex and long paleocanyon-cutting history teau, where more than 3 km of section have been work (Fig. 1A). These faults have acted as path- spanning the Cenozoic (cf. Polyak et al., 2008; removed in areas (Nuccio and Condon, 1996; ways for fl uid fl ow, resulting in a set of aban- Karlstrom et al., 2008; Wernicke, 2011; Flowers Pederson et al., 2002; Hoffman et al., 2011; Karl- doned and modern spring-travertine mounds and Farley, 2012). However, the southwest mar- strom et al., 2012). The patterns of incision and focused along the fault traces (Shipton et al., gin contrasts with the core of the Colorado Pla- their relation to these distinct potential sources of 2004; Dockrill and Shipton, 2010; Kampman teau physiographic province, including our study regional uplift and other controls are also highly et al., 2012). The travertine mounds themselves area, which has a notably younger and more debated (e.g., Karlstrom et al., 2012; Pederson have been incised, permitting detailed study active record of erosion and landscape evolution and Tressler, 2012; Darling et al., 2012; Pederson of their internal chronostratigraphy (Burnside (Hoffman et al., 2011; Pederson et al., 2013). et al., 2013), but there are few well-constrained et al., 2013), which may constrain Quaternary geomorphic records available in the heart of the movement on these structures. Yet, no solid geo- Colorado Plateau to address these problems. morphic constraints on the timing and rates of *Current address: School of Geosciences, Univer- An exception to the general lack of deforma- faulting have been reported for the region. sity of Edinburgh, Scotland EH9 3JW, UK. †Current address: Department of Civil and Environ- tion in the Colorado Plateau is the episodic salt River terraces are valuable markers for these mental Engineering, University of Strathclyde, Scot- tectonics in the central plateau linked to unload- tectonic geomorphology problems, enabling us land G4 0NG, UK. ing of Pennsylvanian evaporite deposits of the to quantify rates of erosion, faulting, and land- LITHOSPHEREFor permission to| Volumecopy, contact 5 | Number [email protected] 5 | www.gsapubs.org | © 2013 Geological Society of America 513 Downloaded from https://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/5/5/513/3045189/513.pdf by Utah State University Libraries user on 17 October 2019 PEDERSON ET AL. 110 o 15’ W 110o W A mouth of Deso-Gray Canyon Book Cliffs 39 N town of o Green River fault B sh 70 Wa B and Little Gr Salt Valley graben Salt Wash graben Green River Green River KILOMETERS anticline 0 0.5 1 38 45’ N 38 45’ CONTOUR INTERVAL 40 FEET o Moab fault 4200 Labyrint KILOMETERS Canyon 0 5 10 h 4400 Little Grand Wash fault Crystal Geyser 7 Figure 1. (A) Location of the Crystal Geyser study area in the north- 0 central Colorado Plateau of the western United States, near the 420 6 5 2 5 town of Green River in the plateau badlands downstream of the mouth of Desolation–Gray Canyon and the Book Cliffs and upstream of Labyrinth Canyon. (B) Generalized fl uvial terrace levels (num- 5 4 bered) where the Green River crosses the Little Grand Wash fault. 3 1/Qal Detailed mapping results are presented in Data Repository item 1 (see text footnote 1). scape evolution. The trunk drainages of the pla- incision at a location in the north-central Colo- nate the patterns of erosion and deformation in teau have locally preserved a sequence of grav- rado Plateau where such constraints are missing. this landscape. elly strath (thin sediment cover) and thick fi ll We utilize the archive of Green River terrace terraces that record both incision and responses deposits and associated travertine near Crystal BACKGROUND to climate change (e.g., Marchetti and Cerling, Geyser, at the intersection of the Green River 2005; Pederson et al., 2006). Through strati- and the Little Grand Wash fault (Fig. 1B; DR1 Setting graphic and geochronologic study, these can be map1). Field and geochronology results at Crys- used to constrain rates of local faulting and also tal Geyser reveal clear evidence for active river The Crystal Geyser study area lies along the provide time-integrated rates of incision along incision, but not active faulting, helping illumi- Green River, 7 km south of the town of Green the trunk drainages that set the pace for broader 1GSA Data Repository Item 2013319, a 1:12,000 scale surfi cial geologic map of the study area (item 1) and erosion in the landscape. tables, graphs, and descriptions of luminescence methods and results (item 2), is available at www.geosociety The goal of this study is to document any .org/pubs/ft2013.htm, or on request from [email protected], Documents Secretary, GSA, P.O. Box 9140, late Quaternary faulting and the rate of river Boulder, CO 80301-9140, USA. 514 www.gsapubs.org | Volume 5 | Number 5 | LITHOSPHERE Downloaded from https://pubs.geoscienceworld.org/gsa/lithosphere/article-pdf/5/5/513/3045189/513.pdf by Utah State University Libraries user on 17 October 2019 River incision and faulting in the central Colorado Plateau | RESEARCH River, Utah (Fig. 1A). Flowing to the south, the tine and fault relations, previous workers have past level of the main-stem Green River (DR1 river exits Desolation–Gray Canyon through the proposed some amount of late Pleistocene fault map [see footnote 1]; P6/5 on cross section in Book Cliffs upstream and crosses low-relief, movement on the Little Grand Wash fault (Wil- Fig. 2; Table 1). arid badlands underlain by the upper Creta- liams, 2004; Shipton et al., 2004). ceous Mancos Shale before entering Labyrinth Crystal Geyser itself is a periodic, CO2- METHODS Canyon downstream of the study area. As the charged geyser created by an oil exploration river approaches the Little Grand Wash normal well drilled in A.D.